The invention relates to steering columns for motor vehicles, which comprise an energy-absorbing device which becomes effective in the event of an impact of the motor vehicle.
A steering column is a component of the steering mechanism in motor vehicles. The steering column is typically a rod- or tube-shaped carrier which is connected at the upper end to the steering wheel and transmits the movements of said steering wheel to the steering linkage of the vehicle wheels. The steering column is located in the centre in front of the driver's seat and extends inclined from the position of the steering wheel towards the front downwards to the steering linkage.
As in the case of the steering column of the type mentioned above, steering columns are embodied in the manner of a telescope, so that in the event of a frontal impact of the motor vehicle the steering wheel can be displaced away from the driver, by virtue of parts of the steering column sliding one inside the other in a decelerated manner, in order to alleviate the consequences for the driver when impacting the steering wheel.
For this purpose, the steering column of the type mentioned above is provided with at least one energy-absorbing device which becomes effective in the event of an impact of the motor vehicle.
A steering column in accordance with DE 10 2005 052 123 B3 comprises two energy-absorbing devices which become effective in the event of an impact of the motor vehicle and are arranged, offset by 180° around the longitudinal direction of the steering column, on the steering column casing tube. Each of the two devices comprises a first element which is embodied as an elongated metal plate in which is embodied an elongated hole. A second element engages with the first element, the second element being embodied as a bolt which engages in the elongated hole of the first element. The elongated hole of the first element extends in the longitudinal direction of the steering column. The bolt which is arranged in the manner of a slider in the elongated hole comprises an elongated round shape, wherein a guide element in the form of a lateral enlargement is embodied respectively on the two longitudinal edges of the bolt. During normal operation of the motor vehicle, the first element and the second element are located in a rest position, in which the lateral enlargements of the bolt protrude into enlargements of the elongated hole of the first element, thus producing an at least partial form fit. The bolt is prevented in this manner from displacing with respect to the elongated hole during normal operation.
In the event of an impact of the motor vehicle (also referred to as a crash), the bolt deforms the elongated hole, in that the lateral enlargements of the bolt expand the elongated hole, while the bolt is displaced in the elongated hole relative thereto. Thus, in the case of this device, the steering column moves one inside the other in a telescopic and decelerated manner, causing the steering wheel to move away from the driver. Thus, the bolt executes deformation work on the first element, in that the bolt expands the elongated hole transverse to the longitudinal direction, as a result of which mechanical energy from the impact is absorbed.
However, the energy-absorbing devices of the known steering column have disadvantages.
As a result of embodying the first element as a metal plate with an elongated hole, which is through-going perpendicular to the plane of the metal plate and extends in the longitudinal direction of the metal plate, the metal plate is provided between its longitudinal ends with two material webs which extend in the longitudinal direction and are relatively thin. If this metal plate is now welded, for example by laser welding, for example to the casing tube which surrounds the steering wheel shaft, it is possible that the aforementioned material webs of the metal plate distort, as a result of which the mutual spacing between the material webs and at the same time the hole width of the elongated hole is reduced or enlarged at some locations over the length of the metal plate. This means that the width of the elongated hole, as seen over the length of the metal plate, is subject to excessive tolerances which accompany corresponding tolerances in the absorption of impact loading and thus the energy absorption.
In addition, the embodiment of the energy-absorbing device of the known steering column has the disadvantage not only that excessive tolerances are produced by the fastening of the metal plate to the underlying material, but also that it is not easy to control the process of implementing the elongated hole in the metal plate with respect to tolerances.